listbox拖动排序

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApplication4
{
    public partial class Form1 : Form
    {
        int indexofsource;//拖动的起始索引
        int indexoftarget; //拖动的结束索引
        public Form1()
        {
            InitializeComponent();
        }

        private void listBox1_MouseDown(object sender, MouseEventArgs e)
        {
            indexofsource = ((ListBox)sender).IndexFromPoint(e.X, e.Y);
            if (indexofsource != ListBox.NoMatches)
            {
                ((ListBox)sender).DoDragDrop(((ListBox)sender).Items[indexofsource].ToString(), DragDropEffects.All);
            }

        }

        private void listBox1_DragOver(object sender, DragEventArgs e)
        {
             if (e.Data.GetDataPresent(typeof(System.String)) && ((ListBox)sender).Equals(listBox1))
            {
                e.Effect = DragDropEffects.Move;
            }
            else
                e.Effect = DragDropEffects.None;

        }

        private void listBox1_DragDrop(object sender, DragEventArgs e)
        {
            ListBox listbox = (ListBox)sender;
            indexoftarget = listbox.IndexFromPoint(listbox.PointToClient(new Point(e.X, e.Y)));
            if (indexoftarget != ListBox.NoMatches)
            {
                string temp = listbox.Items[indexoftarget].ToString();
                listbox.Items[indexoftarget] = listbox.Items[indexofsource];
                listbox.Items[indexofsource] = temp;
                listbox.SelectedIndex = indexoftarget;
            }

        }
    }
}